post api pblm in backend

Question

    const newItem = { name, price, img, detail, email }

    fetch("http://localhost:5000/add", {
        method: "POST",
        header: {
            "content-type": "application/json"
        },
        body: JSON.stringify(newItem)
    })
    .then(res => res.json())
    .then(data => {
        if (data.acknowledged === true) {
            toast.success('Product add Successfully')
            event.target.reset()
            return;
        }
     })

my code does not work. I want to create a post api in my backend server. I send post request from my client side but doesn't work.